This invention relates to a method of controlling the operating amount of an operation control means for an internal combustion engine, and more particularly to a method of this kind which is adapted to set a desired operating amount for an operation control means, which is optimal to an operating condition of the engine in a predetermined low region, to thereby achieve smooth operation of the engine.
A method has been proposed, e.g. by Japanese Provisional Patent Publications (Kokai) Nos. 57-137633 and 53-8434, which determines a basic operating amount of operation control means for controlling the operation of the engine, such as a basic fuel injection amount to be supplied to the engine by a fuel supply quantity control system, a basic value of ignition timing to be controlled by an ignition timing control system, and a basic recirculation amount of exhaust gases to be controlled by an exhaust gas recirculation control system, in dependence on values of engine operating parameters indicative of loaded conditions of the engine, such as absolute pressure in the intake pipe of the engine and engine rotational speed, and corrects the basic operating amount thus determined in response to the temperature of intake air, the temperature of engine cooling water, etc., to thereby set a desired operating amount for the operation control means with accuracy.
Further, it is also known to design the intake pipe of the engine, particularly a portion thereof downstream of a throttle valve therein, to have a large volume enough to increase the charging efficiency of intake air, thereby achieving improved operating characteristics of the engine, such as increased output of the engine.
However, to increase the volume of the intake pipe at a portion downstream of the throttle valve causes a reduced rate of change in the intake pipe absolute pressure relative to the lapse of time with respect to a rate of change in the engine speed relative to the lapse of time, while the engine is operating in a low load condition, such as at idle. Therefore, with the above-mentioned proposed method of determining operating amounts of the operation control means in dependence on the intake pipe absolute pressure and the engine speed (generally called "the speed density method", and hereinafter merely referred to as "the SD method"), it is difficult to set with accuracy an operating amount such as a fuel supply quantity in accordance with operating conditions of the engine, thus causing hunting of the engine rotation. In view of the foregoing, a method (hereinafter merely called "the KMe method") has been proposed, e.g. by Japanese Patent Publication No. 52-6414, which is based upon the recognition that the quantity of intake air passing the throttle valve is not dependent upon pressure PBA in the intake pipe downstream of the throttle valve or pressure of the exhaust gases while the engine is operating in a particular low load condition wherein the ratio of intake pipe pressure PA' upstream of the throttle valve to intake pipe pressure PBA downstream of the throttle valve is below a critical pressure ratio (=0.528) at which the intake air forms a sonic flow, and accordingly the quantity of intake air can be determined solely in dependence on the valve opening of the throttle valve. Therefore, this proposed method detects the valve opening of the throttle valve alone to thereby detect the quantity of intake air with accuracy while the engine is operating in the above-mentioned particular low load condition, and then sets an operating amount such as a fuel injection quantity on the basis of the detected value of the intake air quantity.
However, if, for instance, the manner of setting the fuel injection quantity is promptly switched from the SD method to the KMe method immediately when the engine enters the above particular low load condition from a condition other than the particular low load condition, an abrupt change can occur in the fuel injection quantity to even cause engine shock and engine stall.
Further, an idling rpm control method is disclosed, e.g. in U.S. Pat. Ser. No. 491,208 assigned to the assignee of the present application, which is adapted to maintain the idling speed of the engine at a constant value by controlling the quantity of supplementary air being supplied to the engine through an auxiliary air passage bypassing the throttle valve, and which is also adapted to improve the startability of the engine in a cold condition by controlling the idling speed to a higher value than a desired value for normal temperature idling operation, in such cold condition. Thus, when the intake air being supplied to the engine is formed by not only air passing the throttle valve but also supplementary air passing a control valve arranged in the auxiliary air passage bypassing the throttle valve, the total quantity of intake air being supplied to the engine cannot be detected merely through detection of the valve opening of the throttle valve alone. Therefore, it is not possible to set with accuracy the operating amount of an operation control means, such as a fuel injection quantity, by the above KMe method.